In modern rotary machinery, bearing assemblies are one of the most important component parts. Low friction operation and reliability are two of the key attributes when OEM manufacturers specify a particular bearing assembly for a product. Another important factor, but one that is sometimes overlooked, or at least not given as much attention as the others, is the ease of installation of the bearing assembly on the shaft, as well as the stability of the locking attachment to the shaft.
As further background, the typical bearing assembly includes an inner race that is locked to and rotates with a shaft. A separate outer race is fixedly connected to a supporting structure, such as the equipment framework or body. Smooth and efficient rotary motion of the inner race within the fixed outer race is achieved by interposing between the inner and outer races a plurality of bearing elements, such as rollers or balls. In other instances, a shaft (or spindle) and inner race may be fixed, and the outer race and a rotary element can then freely rotate.
Several arrangements exist for mounting and locking the inner race of a bearing to a shaft. One such method for effecting this function, and which is used in the vast majority of applications, is press fitting. In order to secure the inner race of the bearing to the shaft by press fitting, first the shaft is manufactured with a slightly oversized cross-sectional diameter as compared to the diameter of the inner race, or vice-versa. The shaft is then forcibly fit into the inner race to effect the tight frictional engagement therewith.
Locking the inner race of the bearing to the shaft by means of press fitting has suffered several shortcomings in the past. First, over time and upon extended use, the metals of the inner race and the shaft tend to seize together making bearing replacement difficult or even impossible. In addition, in order to effectively lock the inner race and shaft together by means of press fitting, these parts must be machined to very close tolerances, often within a few ten-thousandths of an inch. It is sometimes even necessary to heat the inner race of the bearing to cause it to temporarily expand to make it easier to slip over the end of the shaft. In these ways, and in other ways, such limitations result in more expensive bearing component and bearing assembly manufacturing costs. Not only is there intricate machining and heating requirements, but there is the intrinsic high reject rate of parts and finished assemblies. In addition, and perhaps most significantly, there are several manufacturing environments that have proven to be unable to effectively use the press fitting approach.
For example, in the field of modular conveyor systems, there currently exists a need for a low cost, but highly efficient system for mounting the roller/ball bearing assemblies on the drive and support shafts. Because of the enumerated engineering shortcomings identified above, it is desired that the system not involve the press fit concept in any manner. Not only is quick and easy installation important, but also easy removal for replacement is a major concern.
Another method used in the industry to secure the inner race of a bearing to a shaft is the utilization of set screws. In such an arrangement, one or more set screws extend through the inner race so as to engage the face of the shaft. Upon tightening of the set screws, the inner race is in effect clamped and secured to the shaft and rotation relative to the shaft is prevented. This arrangement also in practice exhibits several difficulties and shortcomings. First, in order to allow for the insertion of screws through the inner race, it necessarily is of a substantially greater width and extends well beyond the width of the outer race. Accordingly most set screw type bearing assemblies are wider and less compact than those bearing assemblies utilizing other securing methods. In addition, during extended industrial use, especially in environments where a fair degree of vibration is present, such as in modular conveyor systems, retaining the set screws in place is proven to be a difficult task. Upon being exposed to such vibrations, the set screws inevitably tend to loosen and oftentimes disengage causing the undesirable uncoupling of the drive shaft from the inner race of the bearing. Additionally, the set screws tend to score and gouge the shaft making maintenance procedures more difficult, and this condition even contributes to weakening of the shafts in certain installations. Further, because bearing assemblies using set screws provide contact between the inner race and the drive shaft in only a limited number of points, maximum grip between the inner race and the shaft is not achieved.
In an apparent effort to overcome the difficulties realized with these more common set screw securing devices, eccentric locking collars have also been invented and used in conjunction with the inner race to fixedly lock it onto the shaft. An arrangement of this type is disclosed, for example, in U.S. Pat. No. 4,229,059 to Dever. In such a locking arrangement, the inner race of the bearing is provided with a groove having an eccentric inner diameter in an extension of the inner race. Initially, the inner race of the bearing assembly is placed on the shaft. Next, an eccentric ring is placed in the groove. The eccentric ring has a relatively thick portion which is received in a relatively deep portion of the inner race groove. Next, a spanner wrench is used to rotate the inner race of the bearing with respect to the ring and the shaft, so as to clamp and lock the shaft with the inner race of the bearing assembly. Set screws are still needed to secure the eccentric ring, and thus the inner race, in position.
This basic configuration of eccentric ring locking devices also exhibits notable shortcomings. First, the set screws of the eccentric ring are similarly prone to vibrating loose as the prior art screw configurations. Additionally, an axially elongated inner race is still required and relatively complex machining requirements are still necessary to use a locking device of this type.
A variation of the basic eccentric ring locking mechanism is disclosed in the U.S. Pat. No. 3,924,957 to Camosso. According to this arrangement, the eccentric ring incorporates two locking elements. These locking elements slide towards each other along the eccentric portions of the ring to secure the bearing assembly in place. The shortcomings of this arrangement are much the same as the basic eccentric ring locking devices. Specifically, having to use two interacting elements in addition to the ring, simply means that additional parts are required and prone to working loose over time. Additionally, since the Camosso arrangement necessitates the use of an extended inner race, it is also incapable of use in those manufacturing situations where there are space constraints.
Thus, it is clear that a need exists for a bearing assembly with an improved locking mechanism. Such a bearing assembly would be relatively easily machined and manufactured, would eliminate the need of set screws and would generally minimize the number of parts required to reduce the susceptibility to becoming loose due to mechanical vibrations. The need also exists for such a bearing assembly that is adaptable to those situations where there are space constraints.